Learn Portuguese (Portugal): Fiquei de arranjar o candeeiro.

When you use the verb ficar followed by the preposition de and an infinitive verb (like arranjar), it creates a very common expression that means "to agree to", "to promise to", or "to commit to" doing something.

Doesn't arranjar usually mean "to arrange" or "to get"?

It can mean "to arrange" or "to get" (for example, arranjar um emprego means "to get a job"). However, in everyday Portuguese, arranjar is also the most common way to say "to fix" or "to repair" something that is broken.

If I wanted to say "He agreed to fix the lamp", how would this sentence change?

You would simply change the conjugation of the main verb to the third-person singular past tense. It becomes Ficou de arranjar o candeeiro. The rest of the structure (de + infinitive) stays exactly the same.

I often confuse the words for "lamp" and "lightbulb". Does candeeiro mean the whole lamp?

Yes! The word candeeiro refers to the actual lamp or light fixture (whether it is a desk lamp, floor lamp, or ceiling light). If you are talking about the lightbulb that goes inside it, you must use the word lâmpada.